This application is based upon and claims benefit of priority of Japanese Patent Application No. Hei-10-252754 filed on Sep. 7, 1998, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a radio communication device such as a portable telephone that operates under the code-division multiple access system (CDMA), and more particularly to such a device, the communication speed of which is controlled according to temperature of its transmitting amplifier.
2. Description of Related Art
Digital radio communication devices that operate under the time-division multiple access (TDMA) system or under the code-division multiple access (CDMA) are widely used. In high speed communication using a portable packet communication device that operates under the TDMA system, data transmission is performed by continuous time slots. However, if the data transmission is continuously performed, temperature of the transmitting amplifier tends to rise excessively due to high power consumed in the high speed continuous transmission. In case the amplifier temperature exceeds a permissible level, components such as power transistors constituting the amplifier may be damaged by the excessive heat.
To cope with this problem, JP-A-9-326749 proposes a device that operates in the following manner. The device disclosed therein is a portable device for packet communication operating under the TDMA system. In this device, whether TDMA radio time slots are used continuously or intermittently is determined, based on the transmitting amplifier temperature detected by a sensor or information of the TDMA radio time slots used in transmission. Since continuous or intermittent transmission is selectively switched based on the transmitting amplifier temperature, the temperature rise in the device is limited to a certain level even if the data transmission is performed for a long period of time. In this manner, the components of the device such as power transistors are protected from being damaged by excessive heat.
Under the CDMA system, as in the TDMA, a higher transmitting power is consumed as the communication speed increases, as shown in the graph of FIG. 4. Accordingly, the transmitting amplifier temperature becomes higher according to the transmitting speed. If high speed transmission is performed continuously for a long period of time, there is a possibility that the device be damaged due to excessive heat generated in the transmitting amplifier. Under the TDMA, if there is a period in which no transmission is performed by using the radio time slots intermittently, it does not give inconvenience to a user, because the data transmitted are packet data. On the contrary, since the data transmitted under the CDMA are real time data, communication between users are hindered if there is a period in which no data transmission is performed.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide a radio communication device, such as a portable telephone device, that is able to perform high speed communication, while avoiding excessive temperature rise in the device and discontinuation of communication between users.
A portable telephone device operating under the CDMA includes a receiver-transmitter that receives and transmits high frequency signals, a voice processor connected to a speaker and a microphone, an image processor connected to a display panel and a camera, a key pad for inputting command signals, and a controller that controls the operation of the whole device. Generally, high transmitting power is consumed, and temperature of a transmitting amplifier becomes high, when communication is performed at a high speed. A temperature detector for detecting the transmitting amplifier is disposed in the receiver-transmitter.
When the transmitting amplifier temperature is lower than a predetermined first temperature, communication speed of the device is set at a high speed, e.g., 64 kbps. When the transmitting amplifier temperature exceeds the first temperature during operation at the high speed, the communication speed is automatically switched to a low speed, e.g., 8 kbps to avoid overheating of the device. After the transmitting amplifier temperature becomes below a predetermined second temperature that is lower than the first temperature during operation at the low speed, the communication speed is automatically switched again to the high speed.
Both of the voice and image data are transmitted during the period in which communication is performed at the high speed. When the communication speed is switched to the low speed to avoid overheating of the device, only the voice data are transmitted and transmission of the image data is cut off, because the low speed is insufficient to transmit both the voice and image data. When the communication speed is switched back again to the high speed, transmission of both the voice and image data are resumed.
According to the present invention, the communication device is protected from overheating while keeping the communication speed as high as possible without interrupting communication.